The present invention relates to color-stable polymeric films and products made therefrom. More particularly, the present invention relates to color-stable pigmented polymeric films made of a polyester.
Tinted polymeric films, and particularly tinted polymeric films made of a polyester, find utility in a broad range of applications. These films, for example, can be applied to a base transparent substrate (e.g., a window or auto glass pane) to provide a neutral color tint to the window or auto glass. They can also used to tint the surface of a display device, mirror, or other piece of optical equipment.
One method for tinting a polymeric base film employs dyeing the base film with one or more color dyes. Typically in such methods, the neutral color, or xe2x80x9ctint,xe2x80x9d is obtained by imbibing (or blending) the base film material with a combination of yellow, red and blue dyes. While these dyed films generally retain a high clarity and a low haze, prolonged exposure to ultraviolet radiation (which occurs naturally during outdoor use or by exposure to fluorescent light or other UV-emitting light source) can cause significant degradation of the dye molecules and lead to tinting color alteration, tinting power deterioration, bleachings, and reduced light transmission.
Another method sometimes employed for tinting a polymeric film is to apply a pigmented coating to the surface of a base polymeric film. Generally, such coatings are applied as thin layers and employ a relatively high pigment concentration to achieve a desired tint level. These highly-concentrated pigment coatings can suffer myriad processing and performance drawbacks. For example, the high pigment concentrations necessary to achieve requisite tinting strengths are difficult to uniformly disperse within the thin coating, and these high surface pigment concentrations generally suffer faster environmental deterioration. Moreover, such pigmented coatings typically suffer greater haze and reduced clarity.
There exists, therefore, a need for a pigmented film that is environmentally stable (i.e., color-stable or colorfast), that is easily manufactured and that exhibits low haze and high clarity.
Briefly, in one aspect, the present invention provides a color-stable, pigmented optical body, the optical body comprising: a single or multiple layer core comprising at least one layer of a thermoplastic polymer material having dispersed therein a particulate pigment, wherein the optical body exhibits a transmission of light within a wavelength band of interest within the visible spectrum of from about 10 to about 90 percent and exhibits less than or equal to about five percent internal haze.
In one aspect, the present invention provides a color-stable, pigmented optical body, the optical body comprising: a single or multiple layer core comprising at least one layer of a thermoplastic polymer material having dispersed therein a particulate pigment, wherein the optical body exhibits an average transmission of light within the visible spectrum of from about 10 to about 90 percent and exhibits an internal haze of less than or equal to about five percent.
In yet another aspect, the invention provides a color-stable, pigmented optical body comprising a single or multiple layer core comprising at least one layer of a thermoplastic polymer material, wherein dispersed within the thermoplastic polymer material is between 0.01 and about 1.0 percent by weight of a particulate pigment having a mean diameter of between about 10 nm and 500 nm, and wherein the optical body exhibits a transmission of light within a wavelength band of interest within the visible spectrum of from about 10 to about 90 percent.
In still another aspect, the invention provides a color-stable, pigmented optical body comprising a single or multiple layer core comprising at least one layer of a thermoplastic polymer material having dispersed therein a particulate pigment, wherein the optical body has a surface roughness, Ra, of less than or equal to about 60 and exhibits a transmission of light within a wavelength band of interest within the visible spectrum of from about 10 to about 90 percent.
The invention also provides a method of making a color-stable, pigmented optical body, the method comprising:
(a) creating a substantially uniform dispersion of a particulate pigment having a mean diameter of between about 10 nm and about 500 nm;
(b) adding the dispersion to a reaction mass of a condensation polymer forming process, wherein the dispersion is present in an amount sufficient to impart a transparency to the optical body between about 10 and 90 percent;
(c) reacting the condensation polymer forming reaction mass to form a condensation polymer having dispersed therein the particulate pigment; and
(d) forming an optical body comprising at least one layer of the condensation polymer.
In still other aspects, the present invention provides articles, including pigmented window and auto glass films, that incorporate the above color-stable optical bodies.